Reverse optical mastering for data storage disks

ABSTRACT

A data storage master disk and method of making a data storage master disk. The data storage disk master is for use in a data storage disk replication process. The data storage disk molding processes produces replica disks having a surface relief pattern with replica lands and replica grooves. The method includes providing a master substrate. The master substrate is at least partially covered with a layer of photosensitive material. A surface relief pattern having master lands and master grooves is recorded in the data storage disk master, including the steps of exposing and developing the photosensitive material. The exposing and developing of a specified thickness of photosensitive material is controlled to form master grooves extending down to a substrate interface between the master substrate and the layer of photosensitive material, such that the width of the master grooves at the substrate interface corresponds to a desired width of the replica lands.

This application is a continuation-in-part of application Ser. No.09/055,825, filed on Apr. 6, 1998, now abandoned.

TECHNICAL FIELD

The present invention relates generally to the field of manufacture ofoptical data storage disks, and in particular, to an optical diskmastering process for use in a disk molding process, capable of moldingdata storage disks containing a high density of information.

BACKGROUND OF THE INVENTION

Optical disks are produced by making a master which has a desiredsurface relief pattern formed therein. The surface relief pattern iscreated using an exposure step (e.g., by laser recording) and asubsequent development step. The master is used to make a stamper, whichin turn is used to stamp out replicas in the form of optical mastersubstrates. As such, the surface relief pattern, information andprecision of a single master can be transferred into many inexpensivereplica optical disk substrates.

During the mastering exposure step, the mastering system synchronizesthe translation position of a finely focused optical spot with therotation of the master substrate to describe a generally concentric orspiral pattern of a desired track spacing or “track pitch” on the disk.The generally spiral track forming the desired surface relief pattern asa result of the mastering process can be defined by high regions termed“lands” and lower adjacent regions termed “grooves” and/or pits (i.e.,interrupted grooves). The recording power and size/shape of the focusedoptical spot (spot size) as well as the photosensitive materialparameters determine the final geometry revealed in the master diskduring the subsequent development step. Normal mastering practice useshigh contrast positive photoresist for the photosensitive material.

Conventional mastering typically utilizes laser light with wavelength,λ, in a range of 350 nm<λ<460 nm focused through an objective with anumerical aperture (NA) of 0.75<NA<0.90 to give a theoretical Gaussianspot size of:SS=0.57λ/NA (full width at half maximum intensity (FWHM)).Thus, a 350 nm laser light with NA=0.9 gives a theoretical spot size0.22 microns (FWHM) as the practical limit for conventional optics.

After the master is recorded, it is flooded with developer solution toreveal the exposure pattern applied by the master recording system. Thedissolution of the photoresist in the developer solution is inproportion to the optical exposure previously received in the recordingprocess. The dissolution rate of the photoresist can be modeled forgiven exposure and development conditions (see Trefonus, P., Daniels,B., “New Principal For Imaging Enhancement In Single Layer PositivePhotoresist”, Proc. of SPIE vol. 771 p.194 (1987), see also Dill F. etal., “Characterization of Positive Photoresists” IEEE Transactions onElectronic Devices, vol. ED-22 p. 445 (1975).) Expressions explained inthese referenced technical papers can be used to model the effects ofexposures from several adjacent tracks recorded in the photoresist andsubsequently developed. The photoresist dissolution in the developersolution is in proportion to the optical exposure previously received(positive type resist). More accurately, the dissolution rate (R) isgiven by the Trefonas model asR[nm/sec]=R ₀×(1−M)^(q) +R _(b)Where R₀ and R_(b) are the dissolution rates of the fully exposed andunexposed photoresist (respectively), q is a resist parameter related tothe resist contrast and M is the fractional unconverted photoactivecompound in the resist. Typical values for commercially availableresists are q=3, 10<R₀<200 [nm/sec] and R_(b)=0 for normal developerconcentrations. The M term is dependent in a point-wise fashion on howmuch exposure was received in the resist (E(x,y,z)) and the resist'sparametric sensitivity “C” per the Dill convention:M(x,y,z)=exp{−C×E(x,y,z)}.

Since optical disk mastering typically uses only 50-200 nm ofphotoresist thickness, the z-dependence of exposure can safely beignored so that the above equations can be combined to giveR=R ₀(1−exp{−CE(x,y,)})^(q);or, with the exposure profile explicitly circular gaussian we maysimplify to R=R ₀(1−exp{−CkP exp[−r ² /SS ²]})^(q);Where r measures the radial distance from the center of the spot(r²=x²+y²), P is the recording power and k is a normalization constantfor the guassian function. This dissolution rate, multiplied by thedevelopment time (t_(d)), gives the depth of photoresist lost from itsinitial coating thickness (T₀), so that the final resist thickness(T(t)) is given by T(td)=T₀−t_(d) R₀ (1−exp{−CkP exp[−r²/SS²]})^(q);From this expression one can see how optical exposure (P), development(t_(d), R₀) and photoresist thickness (T₀) determines final surfacerelief pattern.

In some aspects, these expose/development processes may be compared withconventional photography. In photography, either exposure or developmentmay be controlled/adjusted as necessary to obtain desired finaldevelopment pattern. In this sense, one may consider theexpose/development level as one process variable which may alternativelybe controlled by recording power, development time, developerconcentration, etc.

In the mastering process, it is desirable to simultaneously obtain widelands (for user recorded features) and grooves of suitable depth foradequate tracking signals (e.g., greater than 50 nm). Higher densitydata storage disks often require the storage of a greater amount ofinformation within the same or smaller size of disk area, resulting insmaller track pitch (i.e., distance between tracks) design criteria.

Attempts have been made to meet these design criteria. In prior artFIGS. 1-3, surface relief patterns of exemplary master disks formedusing conventional disk mastering techniques are illustrated using theabove expressions to model the effects of exposures from severaladjacent tracks recorded in the photoresist layer and then developed.These comparisons assume (1) typical photoresist and developerparameters, (2) constant development time (=40 sec.), (3) SS=0.23microns, (4) track pitch of 0.375 microns and initial photoresistthickness of 100 nm. As recording power (or alternatively, developmenttime) is increased to obtain deeper grooves, the residual land widthdiminishes and lands become more rounded due to overlap exposure fromadjacent tracks. Partially developed photosensitive material exhibits agranular roughness greater than that of the photosensitive material asinitially coated on the disk. Roughness of lands worsens with deepeningof grooves, resulting in additional noise in data readback.

More problems occur when the track pitch approaches the finite size ofthe mastering spot size. For formats where the desired track pitch ismuch larger (>2×) than the finite size of the mastering spot size (ss),the photosensitive material erosion of the lands is negligible andconventional mastering can provide wide lands with a >50 nm groovedepth. However, for formats where the track pitch is <2× larger than thespot size, conventional mastering requires a compromise of either landwidth, groove depth, or both (due to overlap exposure from adjacenttracks).

In FIG. 4, exemplary embodiments of the mandatory link between landwidth and groove depth when using conventional mastering processes isillustrated. (Examples of 0.375 micron and 0.425 micron track pitch with0.22 micron recording spot size). As the groove depth increases, theland width decreases. The master surface relief pattern geometries (i.e,land width/groove depth) are constrained for given conditions of trackpitch and mastering spot size. This means the designer may notindependently specify the desired parameters for replica land width andreplica groove depth.

A secondary problem for conventional mastering is that the land widthprecision is limited by mechanical track pitch precision (e.g.,mechanical precision of master recording system), which is increasinglydifficult to control as track pitch decreases.

SUMMARY OF THE INVENTION

The present invention provides a data storage master disk and method ofmaking a data storage master disk wherein the user may independentlyspecify the parameters of replica land width and replica groove depth.The data storage master disk is for use in a data storage disk moldingprocess for producing replica disks which are capable of storing a highcapacity of information using a variety of disk formats.

In a first embodiment, the present invention provides a method of makinga data storage master disk for use in a data storage disk moldingprocess. The data storage disk molding process produces replica diskshaving a surface relief pattern with replica lands and replica grooves.The method includes the step of providing a master substrate. The mastersubstrate is covered with a layer of photosenstive material having aspecified thickness. A surface relief pattern having master lands andmaster grooves is recorded in the data storage master disk, includingthe steps of exposing and developing the photosensitive material. Theexposing and developing of a specified thickness of a photosensitivematerial is controlled to form master grooves extending down to asubstrate interface between the master substrate and the layer ofphotosensitive material, such that the width of the master grooves atthe substrate interface corresponds to a desired width of the replicalands.

The thickness of the photosensitive material is specified and controlledto correspond to a desired depth of the replica grooves. In anotheraspect, the thickness of the photosensitive material is specified andcontrolled in dependence on master recording system spot size, desiredtrack pitch, and desired depth of replica grooves. The step ofcontrolling the exposure and development of the data storage master diskmay include the step of controlling the exposing and developing of thephotosensitive material to obtain a flat master groove bottom. Inanother aspect, the step of controlling the exposure and development ofthe data storage master disk includes the step of controlling theexposing and developing of the photosensitive material to obtain asmooth, flat master groove bottom, with smoothness determined by themaster substrate.

The step of controlling the exposing and developing of thephotosensitive material may include the step of controlling opticalenergy for exposing the photosensitive material to a degree sufficientto obtain a desired master groove bottom width after development andremoval of the photosensitive material. In another aspect, the step ofcontrolling the exposing and developing of the photosensitive materialmay include the step of controlling the development of thephotosensitive material to a degree sufficient to obtain a desiredmaster groove width after development and removal of the exposedphotosensitive material.

The step of exposing and developing the data storage master disk mayinclude the step of forming a groove bottom, wherein the groove bottomis flat relative to the master land. The step of exposing and developingthe data storage master disk results in the data storage master diskhaving a master surface relief pattern defined by the master lands andthe master grooves, wherein the surface relief pattern of the replicadisks has an orientation which is inverse the orientation of the datastorage master disk surface relief pattern.

The present invention may further provide the step of polishing themaster substrate optically smooth; and forming a smooth master groovebottom using the master substrate. In one aspect, the step of providinga master substrate includes forming a master substrate made of glass.Preferably, the glass is polished. The photosensitive material may bebonded to the master substrate with or without intermediate layers.

The present invention may further provide for forming a first stamperusing the data storage master disk. Replica disks are made using thefirst stamper. The step of making replica disks using the data storagemaster disk may be accomplished using a multiple generation stamperprocess.

In another embodiment, the present invention provides a method of makinga replica disk from a master disk using an inverse stamping process. Thereplica disk is capable of storing high volumes of information. Thereplica disk includes a surface relief pattern with replica lands andreplica grooves. The method includes the step of providing a mastersubstrate. At least a portion of the master substrate is coated with alayer of photosensitive material to form the master disk. A surfacerelief pattern having master lands and master grooves is recorded in themaster disk, including the steps of using a laser beam recorder forexposing the photosensitive material in a desired track pattern having atrack pitch, and developing the photosensitive material. The exposingand developing of the photosensitive material is controlled for formingmaster grooves extending down to a substrate interface between themaster substrate and the photosensitive material, such that the width ofthe master grooves at the substrate interface corresponds to a desiredwidth of the replica lands. A first stamper is formed from the masterdisk. A second stamper is formed from the first stamper. A replica diskis formed from the second stamper, the replica disk including a surfacerelief pattern having an orientation which is the inverse of the masterdisk.

The present invention may further provide the step of controlling thethickness of the layer of the photosensitive material to correspond to adesired depth of the replica grooves. The specified and controlledthickness of the photosensitive material depends on master recordingsystem spot size, desired track pitch, and desired depth of replicagrooves.

The step of controlling the exposing and developing of thephotosensitive material may include the step of controlling the exposingand developing of the photosensitive material to obtain a flat mastergroove bottom. Recording a desired track pitch in the photosensitivematerial may further include the use of a focused laser beam at a spotsize which is greater than one half of the track pitch.

The step of a master substrate may include providing a master substratemade of glass. Further, the master substrate may be polished.

In one aspect, the desired track pattern is a spiral track defined byadjacent master lands and master grooves, wherein the steps ofexposing/developing the master disks includes forming a wide, flatmaster groove bottom defined by the disk substrate. The step ofrecording the master disk includes forming master groove bottoms havinga width which does not necessarily depend on the depth of the mastergroove for a desired track pitch. The resulting depth of the mastergroove is dependent on the specified thickness of the photosensitivematerial and the cumulative optical exposure received by thephotosensitive layer at a position half way between two adjacent tracks.In particular, this depends on the desired groove bottom width and theratio of master recording spot size to desired track pitch.

In another embodiment, the present invention provides a master disk. Themaster disk includes a master substrate. A layer of photosensitivematerial covers at least a portion of the master substrate. Thephotosensitive material includes a surface relief pattern in the form ofa track pattern defined by adjacent master lands and master grooves. Themaster grooves extend down to the disk substrate, the master groovesincluding a master groove bottom and the master lands including a masterland top, wherein the master groove bottom is wider than the master landtop.

The master groove bottom is generally flat. In particular, the mastergroove bottom is flat relative to the master land top, and inparticular, the master groove bottoms may be wide and flat relative tothe master land tops. Preferably, the master groove bottoms includesharp corners. Additionally, all of the master groove bottoms on theexposed/developed master disk are level with each other to the precisionof the master substrate flatness. This is important in flying head mediaapplications, such as near field recording techniques, where smalllenses fly in proximity to the replica disk surface.

The master grooves may include a groove depth which is proximate thethickness of the photosensitive material for cases where the track pitchis greater than approximately 1.6 times the spot size. In one aspect,the master grooves include a groove depth which is greater than 50nanometers, track pitch is less than two times the mastering system spotsize, and the width of the master groove bottom is greater than 25percent of desired track pitch. In another aspect, the width of themaster groove bottom is greater than 50 percent desired track pitch.

In another embodiment, the present invention provides a disk including areplica substrate having a first major surface and a second surface. Thefirst major surface includes a surface relief pattern in the form of atrack pattern defined by adjacent lands and grooves. The track patternhaving a track pitch less 0.425 nanometers, wherein the grooves extenddown into the disk substrate. The grooves include a groove bottom andthe replica lands include a land top, wherein the land top is flat. Thisis particularly important in near field recording techniques, whereinlens-to-media-surface separation is extremely critical.

In one aspect, the land top has a width greater than 25 percent of trackpitch. In one preferred aspect for the track pitch less than or equal to400 nanometers, the groove depth is greater than 80 nanometers and theland width is greater than 160 nanometers. Preferably, the land top issmooth and has sharp edges. In one preferred embodiment, the land topsare level with each other to the precision of the flatness of the masterdisk substrate. The land tops are level and at the same elevationrelative to the second major surface. This is important in flying headmedia applications, such as near field recording techniques, where smalllenses fly in proximity to the replica disk surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principals of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as the same become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, in which likereference numerals designate like parts throughout the figures thereof,and wherein:

FIG. 1 is a partial cross section illustrating the surface reliefpattern of a prior art recorded master disk;

FIG. 2 is a partial cross-section illustrating the surface reliefpattern of another master disk made using a prior art recording process;

FIG. 3 is a partial cross-section illustrating the surface reliefpattern of another master disk made using a prior art recording process;

FIG. 4 is a graph illustrating master groove depth versus master landwidth for a master disk made using prior art mastering/recordingtechniques;

FIG. 5 is a plan view illustrating one exemplary embodiment of arecorded master disk made using a data storage disk mastering process inaccordance with the present invention;

FIG. 6 is an enlarged partial cross-sectional view taken along line 6—6of FIG. 5;

FIG. 7 is an enlarged partial cross-sectional view illustrating a stepin making a master disk in accordance with the present invention;

FIG. 8 is a diagram illustrating another step in making a master disk inaccordance with the present invention;

FIG. 9 is a diagram illustrating one exemplary embodiment of the surfacegeometry of a master disk made using the process in accordance with thepresent invention;

FIG. 10 is a diagram illustrating another exemplary embodiment of thesurface geometry of a master disk made using the process in accordancewith the present invention;

FIG. 11 is a diagram illustrating another exemplary embodiment of thesurface geometry of a master disk made using the process in accordancewith the present invention;

FIG. 12 is a graph illustrating maximal master groove depth versusmaster groove bottom width for examples of master disks made using themastering process in accordance with the present invention;

FIGS. 13—18 illustrate experimental atomic force microscope traces ofseveral differing surface relief geometries for master disks recorded at0.375 and 0.425 micron track pitch using the mastering process inaccordance with the present invention;

FIG. 19 is a diagram illustrating groove orientation for replica disksmade from a master disk in accordance with the present invention, usinga multiple generation disk molding/replication process;

FIG. 20 is a block diagram illustrating a data storage disk masteringprocess in accordance with the present invention; and

FIG. 21 is a block diagram illustrating a process for making a replicadisk using a master disk in accordance with the present invention.

DETAILED DESCRIPTION

The present invention includes a data storage master disk and opticaldisk mastering process for making the unique data storage master disk.The process in accordance with the present invention provides for amaster data storage disk having grooves which extend down to the mastersubstrate, resulting in deep, flat, and wide master disk grooves. Themaster disk can be used in a disk molding process which includes areverse mastering/inverse stamping process, resulting in replica diskshaving wide, flat lands with sharp edges, and deep grooves relative toreplica disks formed using conventional mastering processes. As such,the present invention is particularly useful in enabling flexible designof surface relief geometry for molded data storage disks containing ahigh density of information. This includes the ability to create wide,flat land features even in replica disks having a track pitch of lessthan two times the mastering system laser beam spot size.

In FIG. 5, a data storage master disk 20 in accordance with the presentinvention is generally shown. Master disk 20 may be used as part of adisk replication process (e.g., a disk molding process) for producingvarious formats of optical data disks. The data features on the opticaldata disks may include data pits, grooves, bumps or ridges, and land orland areas. This includes current formats of audio CD, CD-ROM and videodisk, such as DVD, as well as future formats which use data featuresdescribed herein. The definition of optical data disks may includevarious types of recordable optical disks (e.g., CDR, magneto-optic, orphase-change disk formats, which commonly use features, such as groovesor pits, for tracking and address identification, even though data issubsequently recorded by the users.

Master disk 20 includes a surface relief pattern (i.e., surfacegeometry) in the form of “data tracks” 22 (shown enlarged for clarity)which may include features representing data encoded therein or whichallow the storage, reading, and tracking of data thereon. Data tracks 22on the optical disk can be arranged in a spiral track 24 originating atthe disk center 26 and ending at the disk outer edge 28, oralternatively, the spiral track 24 may originate at the disk outer edge28 and end at the disk center 26. The data can also lie in a series ofconcentric tracks spaced radially from the disk center 26. Master disk20 may or may not include a center hole, and may be hubbed or hubless.

In FIG. 6, a partial cross-sectional view illustrating one exemplaryembodiment of master disk 20 in accordance with the present invention isshown. Master disk 20 includes data layer 30 and master substrate 32 (aportion of which is shown). The data layer 30 includes a surface reliefpattern shown as data tracks 22. The data tracks 22 are defined by aseries of adjacent master lands 34 and master grooves 36 formed in thedata layer 30 (e.g., which form spiral track 24). The master groovesides 38, 40 are defined by adjacent master lands 34, and include amaster groove bottom 42 which is defined by the master substrate 32.Master substrate 32 provides for a wide, flat and smooth master groovebottom 42.

Data layer 30 is made of a photosensitive material, and more preferably,is made of a photopolymer or photoresist. Master grooves 36 have a depth44 which is equal to the height of master lands 34 relative to mastersubstrate 32, and related to the initial thickness of data layer 30.Master groove depth 44 may further be dependent on mastering spot size,track pitch, and photoresist contrast. Preferably, master grooves 36have a depth greater than 50 nm, and which typically ranges between 50nm and 120 nm. Master groove bottom 42 is preferably flat and smooth asdefined by master substrate 32, having a width 46 which is preferablygreater than 35 percent of the desired track pitch.

In one preferred embodiment, master substrate 32 is made of glass, andis preferably polished and/or optically smooth. The master substrate 32typically varies in thickness between 5 mm and 6 mm. Data layer 30 canbe bonded to master substrate 32. In particular, data layer 30 may becoated directly to master substrate 32 or may include an intermediatelayer (which may be a bonding layer).

The disk mastering process in accordance with the present inventionprovides for master disk 20 having relatively deep master grooves 36with wide, flat master groove bottoms 42. As such, when master disk 20is used in a reverse optical disk mastering process, the master landsand master grooves translate into a replica disk having relatively deepgrooves and wide flat lands. Such characteristics are preferred for manyhigh density and writeable optical disk formats.

The master groove bottoms defined by the disk mastering process inaccordance with the present invention are flat (as opposed to rounded inthe conventional process) with smoothness defined by the mastersubstrate (e.g., polished glass) and includes sharp corners. When usedin connection with an inverse stamping process, this corresponds toreplica disks having wide, flat smooth lands with sharp corners, anddeep grooves. Wide, flat lands are advantageous for positioning userrecorded data thereon. The sharp corners provide domain confinement foruser recorded data (e.g., applications wherein data is magneto-opticallyrecorded on the tops of lands). The wide, flat lands with sharp cornersand deep grooves provide for improved tracking or trackability of themedia substrate. The replica disk land tops are very smooth, due to thegroove bottoms 42 which are defined by the master substrate 32, which ispreferably optically polished glass. The smoothness of the land tops isdefined by the substrate interface between the master substrate 32 andthe layer of photosensitive material 30. Smoothness of land tops resultsin a reduction of noise in subsequent readout of data from the disk.

Further, the wide, flat lands are level with each other, due to thegroove bottoms 42 being defined by the master substrate 32. The flatlands are level with each other and at the same elevation, enhancing theflyability of the disk substrate for flying head applications.

Referring to FIGS. 7 and 8, a method of making an optical disk masterfor use in a data storage disk molding process, in accordance with thepresent invention, is illustrated. In FIG. 7, master substrate 32 isprovided which is preferably made of glass. Master substrate 32typically ranges in thickness between 5 mm and 6 mm. Master substrate 32includes major surface 50. Preferably, major surface 50 is polishedoptically smooth. Major surface 50 is at least partially covered (e.g.,coated) by data layer 30. Data layer 30 may also be coated over anintermediate (e.g., bonding) layer 60 (not shown).

Referring to FIG. 8, master disk 20 is positioned on a master recordingsystem (e.g., a laser recorder or a mask recording system). In oneexemplary embodiment, the master recording system 60 includes controller61, linear translation system 62, master recorder 64, and recordingtable 66. Master recording system 60 provides for controlled exposure ofmaster disk 20 with a focused spot of laser light to encode the desiredsurface relief pattern (i.e., geometry) or data tracks therein.

Master disk 20 is placed on recording table 66, and can be registered(e.g., centered) about a center axis 68, relative to master recorder 64using techniques as known in the art, such as through the use of aspindle, or hubbed master disk 20. Recording table 66 is rotatable aboutthe center axis 68, indicated by rotation arrow 70, for rotation ofmaster disk 20 during the disk recording process. Master recorder 64modulates and focuses a laser beam 72 for exposure of data layer 30 in adesired pattern. Further, master recorder 64 is mechanically coupled tolinear translation system 62 which provides for axial movement of masterrecorder 64 relative to center axis 68, indicated by directional arrow76.

Controller 61 is coupled to linear translation system 62 and masterrecorder 64 (indicated at 61A) and is coupled to recording table 66(indicated at 61B). The controller 61 operates to synchronize thetranslation position of the finally focused laser beam 72 with therotation 70 of master disk 20 to expose spiral track 24 in data layer30. Further, controller 61 may operate to modulate laser beam 72 toexpose pit regions (interrupted grooves) in the header area of the disk.Controller 61 can be a microprocessor based programmable logiccontroller, a computer, a sequence of logic gates, or other device whichmay be capable of performing a sequence of logical operations.

In accordance with the present invention, controller 61 operates tocontrol the optical energy of master recording system 60 for exposingthe photosensitive material of master disk 20 to a degree sufficient toobtain a desired master groove bottom width after development andremoval of the exposed photosensitive material. Controlling the opticalenergy can include controlling either the recording power or controllingthe recording speed for exposing the photosensitive material to a degreesufficient to obtain a desired master groove bottom width afterdevelopment and removal of the exposed photosensitive material. Forexample, controller 61 may operate to increase the recording power ordecrease the recording speed, thereby increasing optical exposure of thephotosensitive material.

The laser recorded master disk 20 is removed from the recording table 66and flooded with a developer solution to reveal the exposure patternprovided by the master recording system 60. The amount of dissolution ofthe data layer 30 in the developer solution is in proportion to theoptical energy previously received during the recording process.Further, the amount of dissolution of the data layer 30 in the developersolution is in proportion to development process parameters, includingthe concentration of the development solution, the development time andtemperature. The type of development solution can be similar todevelopment solutions used in conventional recording processes as knownto those skilled in the art. As such, by controlling the exposure anddevelopment processes, the desired surface relief pattern in thephotosensitive material can be achieved. Since the master recordingsystem 60 was controlled to fully dissolve portions of the data layer 30down to the master substrate 32, the resulting master grooves(previously shown in FIG. 6) include master groove bottoms which aredefined by the master substrate 32 and, in particular, for recordedtrack pitches of less than 2 times the mastering spot size. The abovemaster disk process results in master lands having rounded peaks andmaster grooves having flat, wide and preferably smooth master groovebottoms.

In FIGS. 9-11, exemplary embodiments are shown illustrating the surfacerelief pattern or data tracks for master disks 20A, 20B, 20C which havebeen “overexposed” or “overdeveloped” using the master recording processin accordance with the present invention. With each figure (i.e., FIGS.9-11), the amount of exposure/development of data layer 30 has beenincreased. Referring to FIG. 9, the master recording/developing processresulted in master lands 34A defining master grooves 36A exposed down tomaster substrate 32A. Master grooves 36A have a groove depth of 92 nmwith a corresponding flat master groove bottom 42 having a width of 120nm. Similarly, FIG. 10 illustrates surface relief pattern or data tracks22B having master lands 34B which define master grooves 36B down tomaster substrate 32B. The master grooves 36B have a groove depth of 88nm and a corresponding flat master groove bottom 42 which is 160 nmwide. FIG. 11 illustrates master disk 20C having master lands 34C whichdefine master grooves 36C having master groove bottom 42C defined bymaster substrate 32C. Master groove 36C has a groove depth of 82 nm anda flat master groove bottom 42 which is 200 nm wide. The more masterdisk 20 is overexposed during disk recording process, the greater theerosion of the master lands and wider master groove bottoms areachieved.

In FIG. 12, a graph illustrating the corresponding relationship betweenmaster land width and master groove depth using the master recordingprocess in accordance with the present invention is shown. Usingconventional mastering processes, for a given data layer thickness,master groove depth and master groove bottom width are linked anddependent upon each other (see FIG. 4). Using the mastering process inaccordance with the present invention, by selection of the initialthickness of the data layer and expose/development level, one canindependently specify land width and groove depth. In other words,master groove depth is not dependent upon master groove bottom width,and master groove bottom width is not dependent upon master groovedepth. The two parameters are separable, and by selecting a desired datalayer thickness, and controlling exposure and development criteria, adesired design criteria for the master disk may be obtained.

In the exemplary embodiment shown, plots are shown illustrating designcriteria achieved by increasing initial photosensitive (data) layerthickness (plot 78) and/or increasing exposure energy/development of thephotosensitive layer (plot 79). In all examples, a 0.22 micron spot sizeis assumed. Plot 80 had an initial data layer thickness of 120 nm, plot82 had an initial data layer thickness of 100 nm, plot 84 had an initialdata layer thickness of 80 nm, and plot 86 had an initial data layerthickness of 60 nm. As illustrated, master surface geometries are nolonger constrained by the master land width to master groove depthlinkage as in conventional mastering processes. By starting withdifferent initial data layer thicknesses and controllingexpose/development level, any point within the width-depth parameterspace may be obtained using the disk mastering process in accordancewith the present invention. Whereas FIG. 12 shows how by starting withdiffering initial photosensitive material thickness that any point inthe width-depth parameter space may be obtained, FIGS. 13-18 showcorroborating experimental results illustrated by atomic forcemicroscope (AFM) traces of several differing geometries at 0.375 and0.425 micron track pitch using the disk mastering process in accordancewith the present invention.

The master recording process in accordance with the present invention is(preferably) used in a reverse mastering or inverse stamping process,for creation of replica disks having wide, flat (and smooth) landfeatures at track pitches less than two times the mastering system spotsize. In FIG. 19, a diagram illustrating “groove” orientation of anoptical disk substrate (i.e., a replica disk) molded from a firstgeneration stamper, a second generation stamper or a third generationstamper formed from a master disk in accordance with the presentinvention, is shown. The diagram includes enlarged, partialcross-sections illustrating the orientation of the data tracks of amaster disk 90, first generation stamper 92, second generation stamper94, third generation stamper 96, replica disk substrate 1, replica disksubstrate 2, and replica disk substrate 3. Data tracks are recorded ontothe master disk 90, and have in orientation based on whether a replicadisk substrate is molded from a first, second or third generationstamper.

In particular, master disk 90 includes master data layer 104 havingmaster lands 106 and master grooves 108. First generation stamper 92includes first generation stamper data layer 110 having first generationstamper lands 112 and first generation stamper grooves 114. Secondgeneration stamper 94 includes second generation stamper data layer 116having second generation stamper lands 118 and second generation stampergrooves 120. Third generation stamper 96 includes third generationstamper data layer 122 having third generation stamper lands 124 andthird generation stamper pits 126. Similarly, replica disk substrate 1includes substrate 1 data layer 128 having substrate 1 lands 130 andsubstrate 1 grooves 132; replica disk substrate 2 includes substrate 2data layer 134 having substrate 2 lands 136 and substrate 2 grooves 138;and replica disk substrate 3 includes substrate 3 data layer 140 havingsubstrate 3 lands 142 and substrate grooves 144.

The orientation of substrate 1, data layer 128 molded from firstgeneration stamper 92 corresponds to the orientation of the master diskdata layer 104. In particular, the first generation stamper data layer110 is the inverse of the master disk layer 104. Similarly, replica disksubstrate 1 data layer 128 is the inverse of the first generationstamper data layer 110.

Second generation stamper 94 data layer 116 is the inverse of the firstgeneration stamper 92 data layer 110, resulting in replica disksubstrate 2 data layer 134 being the inverse of second generationstamper 94 data layer 116 and master disk data layer 104. Likewise,third generation stamper 96 data layer 122 is the inverse of the secondgeneration stamper 94 data layer 116. Accordingly, disk substrate 3,data layer 140 is the inverse of the third generation stamper data layer122, and corresponds or has the same orientation as the master disk datalayer 104.

It is recognized that the desired orientation of the master disk datalayer 104 is dependent on the desired orientation of the replica disksubstrate for its intended use. For the example of high-density replicadisks having track pitches less than two times the mastering system spotsize (and air incident media), it is desirable to use a master disk formusing the master disk recording process in accordance with the presentinvention and a second generation stamper process, resulting in areplica disk having wide, flat, smooth lands and deep grooves.Alternatively, for disks read through the substrate, a master diskformed using the master disk recording process in accordance with thepresent invention may be used in a first generation stamper or thirdgeneration stamper process where it is desired to mold a replica diskhaving flat pits or grooves.

In one preferred embodiment, a master disk made using the master diskrecording process in accordance with the present invention is utilizedin a second generation disk molding process. Suitable disk moldingprocesses including one suitable second generation disk molding processcapable of making multiple optical disk stampers from one master disk isas disclosed in U.S. Pat. No. 6,365,329, the disclosure of which isincorporated herein by reference. The above-referenced patent utilizes aunique disk molding process which includes a photopolymerization stepwhich is non-destructive to either the recorded master, first generationstamper or second generation stamper. This allows many next generationsstampers to be made, while maintaining the integrity of the data layertransferred from the previous generation disk. In one embodiment, aportion of a first stamper which defines the data layer is transferredto and becomes part of a second stamper without changing the integrityof the data layer.

Alternatively, other stamper processes may be utilized. For example, inanother exemplary embodiment an electroforming pyramiding family processis used. This process involves the electroforming of a “father” stamperor first generation stamper from a master disk formed using the processin accordance with the present invention. The father stamper is cleaned,treated and returned to the nickel bath to plate a “mother” or secondgeneration stamper. This process cycle can be repeated several times,resulting in multiple “mother” stampers or second generation stamperbeing made from a single father or first generation stamper. The sameelectroforming process may be repeated using the “mother” stamper tomake several “daughter” or third generation stampers from each mother.

In FIG. 20, a block diagram illustrating a process for making a replicadisk using a master disk made in accordance with the present inventionis shown at 110. The master disk is for use in a data storage diskmolding process. The data storage disk molding process produces replicadisks having a surface relief pattern with replica lands and replicagrooves. In the exemplary embodiment shown, the process 110 begins withproviding a master substrate (112). The master substrate is at leastpartially covered with a photosensitive material, which is preferablymade of photoresist (114). A surface relief pattern having master landsand master grooves is recorded in the data storage master disk,including the steps of exposing and developing the photosensitivematerial (116). The exposing and developing of a specified thickness ofphotosensitive material is controlled to form master grooves extendingdown to substrate interface between the master substrate and the layerof photosensitive material, such that the width of the master grooves atthe substrate interface corresponds to a desired width of the replicalands (118).

The master disk can now be used to make a replica disk in a disk moldingprocess. In particular, a stamper is made from the optical master disk(120). A replica disk is made from the stamper (122). The replica diskis capable of storing high volumes of information. In one application,this invention is particularly useful for recording track pitches thatare less than 2 times the master recorder spot size.

In FIG. 21, a block diagram illustrating one exemplary embodiment ofusing a master disk in accordance with the present invention in amultiple generation disk molding process is shown at 130. The masterdisk is fabricated (132) using the unique methods previously describedherein. The methods include exposing and developing the data layer downto the master substrate. A first generation stamper is made from themaster disk (134). A replica disk may be made from the first generationstamper (136).

Alternatively, a second generation stamper is made from the firstgeneration stamper (138). A replica disk is made from the secondgeneration stamper (140). Further, a third generation stamper can bemade from the second generation stamper (142). A replica disk can bemade from the third generation stamper (144).

Photosensitive materials include photopolymers or photoresist, or othermaterials or material blends having similar photosensitivecharacteristics. One group of suitable photosensitive material includesstandard position type high resolution photoresist commerciallyavailable from vendors Shipley, OCG, etc. Other suitable photosensitivematerials may become apparent to those skilled in the art afterreviewing this disclosure.

Suitable photopolymers for use in forming layers, replication layers, orbonding layers discussed herein, include HDDA (4×6×) polyethylenicallyunsaturated monomer-hexanediol diacrylate; chemlink 102 (3×)monoethylenically unsaturated monomer-diethylene glycol monoethyl etheracrylate, elvacite 2043 (1×3×) organic polymer-polyethylmethacrylate,and irgacure 651 (0.1×0.2) latent radicalinitiator-2,2-diamethhoxy-2-phenylacetophenone. Another suitablephotopolymer includes HHA (hydantoin hexacryulate) 1×, HDDA (hexanedioldiacrylate) 1×, and irgacure 651 (0.1×0.2) latent radicalinitiator-2,2-dimethyoxy-2phenylacetophenone. Other suitablephotopolymers may become apparent to those skilled in the art afterreviewing this disclosure.

Numerous characteristics and advantages of the invention have been setforth in the foregoing description. It will be understood, of course,that this disclosure is, and in many respects, only illustrative.Changes can be made in details, particularly in matters of shape, sizeand arrangement of parts without exceeding the scope of the invention.The invention scope is defined in the language in which the appendedclaims are expressed.

The foregoing description describes disk mastering processes for use ina disk molding process. The disk molding process was described in thecontext of creating data storage media such as optical disks havingfeatures such as pits, bumps, ridges, lands, land areas, and/or groovesas defined by the master. The features, in turn, were described as beingthe optically detectable features of an optical disk.

Media having transducer-detectable surface variations may be desirablefor some recording or data storage applications. In some applications,surface variations can be added to contact media and then detected by acontact head. In other applications, surface variations can be added toflying head media such as that contained in a hard drive. The flyinghead used to read the media may be adapted to detect the surfacevariations in addition to (or instead of) magnetic characteristics.

A disk mastering process, as described herein, may be implemented toproduce a suitable master disk for use in a media fabrication processthat produces media having transducer-detectable surface variations.These surface variations may be servo patterns, tracking patterns, dataencoded bumps, pits, rails, lands, grooves, ridges or the like. Forinstance, a master may be created by providing a master substrate,specifying a thickness of photosensitive material, coating the mastersubstrate with the specified thickness of photosensitive material,exposing the photosensitive material to a controlled amount of opticalenergy, and exposing the photosensitive material to a developersolution. The specified amount of photosensitive material, thecontrolled amount of optical energy, and the exposure to developersolution may collectively define an inverse of desired surfacevariations. Moreover, these variables may be collectively controlled sothat the master has a flat groove bottom of a desired width.

Once a suitable master is created, that master may be used to make astamper that stamps surface variations on a medium. In some particularapplications, the medium has a photopolymer layer that is stamped withthe surface variations. Additional layers may be added to the media,such as a hard coat and a lube, such that the additional layerssubstantially conform to the surface variations in the polymer layer. Inthis manner, the surface variations may be exhibited on the surface ofthe medium such that they are transducer detectable. In particular, aflyable magnetic head may be responsive to local temperature or pressurevariations as it flies over the surface variations.

As stated in the description, the disk mastering process may beparticularly advantageous in creating features for flyable media. Forinstance, a second-generation (2G) stamper created from a master, asdescribed herein, may be used to create media with a flyable surface andsurface variations as described above.

Unlike optical lands and grooves, transducer detectable surfacevariations may need a depth less than the head fly height to ensure thatthe media surface exhibiting the variations is still flyable. Forinstance, variations with a depth less than 50 nanometers, or even lessthan 25 nanometers may be necessary. In addition, surface variations mayneed widths less than 150 nanometers to enable highest data storagecapacity. A 2G stamper made from the present mastering process could beeasily used to meet these design criteria. For instance, a mastercreated to have the inverse of the desired surface variations could beused to make a first-generation stamper. The first generation stampercould be used to make a second-generation stamper. The second-generationstamper, then, could be used to stamp the surface variations on replicadisks.

In one specific embodiment, the surface variations may include aplurality of data bumps. These bumps may be circular or oval shaped, forinstance, and one or more may have a surface area less than 50,000square nanometers. These data bumps may project from the medium to aheight less than the fly height, and the height of the bumps may besubstantially uniform. For instance, a medium designed to fly at aheight of 25 nm may have bumps that project from the article a heightless than 25 nm. Bumps of this size may allow significant areal densityof read-only data (>5 Gigabits/in²) while still ensuring that thearticle maintains a flyable surface for a read head. Again, a master asdescribed herein could be used to create a 2G stamper meeting thesedesign criteria with uniform surface variation height as determined byphotosensitive layer coated thickness.

In short, the disk mastering process, described herein, has applicationsfor the creating of a master disk for use in a process that createssurface variations on a data storage medium. The medium may or may notbe an optical medium. Moreover, the medium may be a flyable medium. Forinstance, in one configuration, a magnetic hard disk may have anadditional polymer layer stamped with surface variations. Moreover, theother layers of the hard disk may substantially conform to the stampedpolymer layer. The disk mastering process, described herein, can providea step in the fabrication process of media having transducer detectablesurface variations.

1. A method of creating replica disks that define a desired replicapattern having flat coplanar land tops that define widths in a range ofapproximately 80-200 nanometers and groove depths in a range ofapproximately 20-120 nanometers comprising: focusing light from a laserin a mastering system to form a focused laser spot on a photosensitivemaster, the focused law spot defining a laser spot size, wherein thelaser spot size is defined by a full width at half maximum intensity;laser etching the photosensitive master to form a master pattern that isinverse of the desired replica pattern, the desired replica patterndefining a track pitch less than 2 multiplied by the laser spot sizeassociated with the laser used to perform the laser etching, wherein thetrack pitch is less than approximately 700 nanometers, and wherein thelaser etching defines master groove bottom widths of the master pattern,which correspond to flat coplanar land tops of the desired replicapattern, substantially independently of a master groove depth of themaster pattern; creating a first generation stamper using the master,the first generation stamper having features that are inverted relativeto the master such that the features of the first generation stampercorrespond to the desired replica disk pattern; creating a secondgeneration stamper using the first generation stamper, the secondgeneration stamper having features that correspond to the masterpattern; and creating replica disks using the second generation stamper,wherein the replica disks are formed with the desired replica pattern,which is inverted relative to the master pattern to define the flatcoplanar land tops with widths in the range of 80-200 nanometers and thegroove depths in the range of 20-120 nanometers.
 2. The method of claim1, wherein the desired replica pattern defines a track pitch less than1.6 multiplied by the laser spot size.
 3. The method of claim 1, furthercomprising laser etching the photosensitive master down to a substrateinterface to define flat master groove bottoms that correspond to flatland tops of the desired replica pattern.
 4. The method of claim 3,wherein the flat master groove bottoms define widths greater than 25percent of the track pitch.
 5. The method of claim 3, wherein the flatmaster groove bottoms define widths greater than 35 percent of the trackpitch.
 6. The method of claim 3, wherein the flat master groove bottomsdefine widths greater than 50 percent of the track pitch.
 7. The methodof claim 3, further comprising laser etching the photosensitive musterdown to the substrate interface to define the flat master groove bottomsthat correspond to flat coplanar land tops of the desired replicapattern, wherein the flat coplanar land tops define substantially sharpcorners.
 8. The method of claim 1, wherein the truck pitch is less thanor equal to 400 nanometers.
 9. The method of claim 8, wherein a groovedepth in the master pattern is greater that 80 nanometers and a landwidth of the replica disk pattern is greater than 160 nanometers. 10.The method of claim 1, further comprising: specifying a thickness ofphotosensitive material; and coating a master substrate with thespecified thickness of photosensitive material to form thephotosensitive master; wherein laser etching the photosensitive mastercomprises exposing the photosensitive material to a controlled amount ofoptical energy using the focused light from the laser; and exposing thephotosensitive material to developer solution, wherein the specifiedthickness of photosensitive material, the controlled amount of opticalenergy, and the exposure to developer solution collectively define onthe photosensitive master the inverse of the desired replica pattern.11. The method of claim 1, wherein the desired replica disk patterndefines lands and grooves.
 12. The method of claim 1, wherein thedesired replica disk pattern defines transducer-detectable surfacevariations.
 13. The method of claim 1, wherein the replica diskscomprise flyable media baying flat coplanar replica land tops.
 14. Amethod of creating replica disks that define a desired replica patternhaving flat coplanar land tops that define widths in a range ofapproximately 80-200 nanometers and groove depths in a range ofapproximately 20-120 nanometers comprising: focusing light from a laserin a mastering system to form a focused laser spot on a photosensitivemaster, the focused laser spot defining a laser spot size, wherein thelaser spot size is defined by a full width at half maximum intensityaccording to an equation (constant)(λ)/(NA), where the constant isapproximately equal to 0.57, λ is a wavelength associated with thelaser, and NA is a numerical aperture used in the mastering system; andlaser etching the photosensitive master down to a substrate interface toform a master pattern that is inverse of a desired replica pattern, thedesired replica pattern defining a track pitch less than 2 multiplied bythe laser spot size associated with the laser used to perform the laseretching, wherein the track pitch is less than approximately 700nanometers, and wherein the laser etching defines master groove bottomwidths of the master pattern, which correspond to flat coplanar landtops of the desired replica pattern, substantially independently of amaster groove depth of the master pattern; creating a first generationstamper using the master, the first generation stamper having featuresthat are inverted relative to the master such that the features of thefirst generation stamper correspond to the desired replica disk pattern;creating a second generation stamper using the first generation stamper,the second generation stamper having features that correspond to themaster pattern; and creating replica disks using the second generationstamper, wherein the replica disks are formed with the desired replicapattern, which is inverted relative to the master pattern to define theflat coplanar land tops with widths in the range of approximately 80-200nanometers and the groove depths in the range of approximately 20-120nanometers.
 15. The method of claim 14, the desired replica patterndefining a track pitch less than by the laser spot size.
 16. The methodof claim 15, wherein master groove bottoms are flat and define widthsgreater than 50 percent of the track pitch.
 17. The method of claim 16,wherein the track pitch is less than or equal to 400 nanometers.
 18. Amethod of creating a master comprising: specifying a thickness ofphotosensitive material; coating a master substrate with the specifiedthickness of photosensitive material to form a photosensitive master;focusing light from a laser in a mastering system to a focused laserspot on the photosensitive material of the photosensitive master, thefocused laser spot defining a laser spot size, wherein the laser spotsize is defined by a full width at half maximum intensity according toan equation (constant)(λ)/(NA), where the constant is approximatelyequal to 0.57, λ is a wavelength associated with the laser and NA is anumerical aperture used in the mastering system; exposing thephotosensitive material to a controlled amount of optical energy usingthe focused light from the laser; and exposing the photosensitivematerial to developer solution, wherein the specified thickness ofphotosensitive material, the controlled amount of optical energy, andthe exposure to developer solution collectively define on thephotosensitive master an inverse of a desired replica pattern, thedesired replica pattern defining a track pitch less than 2 multiplied bythe laser spot size of the laser, and wherein the track pitch is lessthan approximately 700 nanometers, and wherein master groove bottomwidths of the master pattern, which correspond to flat coplanar landtops of the desired replica pattern, are substantially independent of amaster groove depth of the master pattern; creating a first generationstamper using the master, the first generation stamper having featuresthat are inverted relative to the master such that the features of thefirst generation stamper correspond to the desired replica disk pattern;creating a second generation stamper using the first generation stamper,the second generation stamper having features that correspond to themaster pattern; and creating replica disks using the second generationstamper, wherein the replica disks are formed with the desired replicapattern, which is inverted relative to the master pattern to define theflat coplanar land tops with widths in the range of approximately 80-200nanometers and the groove depths in the range of approximately 20-120nanometers.
 19. The method of claim 18, the desired replica patterndefining a track pitch less than 1.6 multiplied by the spot size of thelaser.
 20. The method of claim 18, wherein the photosensitive materialcomprises a positive photoresist material and wherein exposing thephotosensitive material to developer solution comprises developing thepositive photoresist material.